[pve-devel] pve-storage : path : add checkaccess param

[Alexandre Derumier]

RPCEnvironnement:check_volume_access only need $path for real file.

Some plugin like nexenta && zfs are doing extra call to api, to find the $path value. (iscsi lun for example).

This can give us big timeouts, as check_volume_access can be call for each volume in a loop when listing volumes.

We want to avoid that, so for theses plugin, if checkaccess param exist, we return empty $path without doing extra calls